For vehicles, industrial trucks and for mobile platforms quite generally, sensor systems are known in order to be able to use an active system to sense the environment and particularly perform distance and/or position measurement. In this case, the distance to objects can be determined from the propagation delay of electromagnetic or acoustic waves. In principle, this involves a signal being sent to a measurement object, from which it is reflected. The time measured for the journey to and fro is used to compute the object distance therefrom. This principle is the basis for ultrasonic systems, for example. In addition, this principle is also the basis for laser distance measurement. Besides distance measurement, it is additionally also possible to determine the direction of an object. Depending on the system configuration, there are several possibilities for this. If the system has a plurality of individual sensors, for example, the direction can be estimated by means of what is known as trilateration. This method is often used for sensors on the bumpers of motor vehicles. If an array having a large number of sensors is used, the direction can also be estimated by means of the phase difference between a plurality of synchronized individual sensors in the array, for example. The German laid-open specification DE 10 2010 062 990 A1 describes an ultrasonic sensor or sound transducer that is suitable for such distance and/or position measurements.
The principle of propagation-delay-based distance and/or position measurement is thus based on the emission of a sound pulse or light pulse into the environment and the capture of the reflected signal as what is known as an echo. In this context, it is important that the echo can also actually be attributed to the emitted signal. This can become a problem when a plurality of units performing distance and/or position measurement on the basis of the same principle encounter one another or are in physical proximity.
There are already various approaches for suppressing or at least reducing such interference. Examples are coding of the transmitted pulses, for example using the respective frequency and/or the amplitude. Another possibility is to apply jitter to the measurement signal repetition rate, that is to say to apply random deviations, as is known from vehicle technology. Other possibilities are an adaptive change of operating frequency or of coding.
The German laid-open specification DE 40 35 501 A1 describes a method for determining the relative position of vehicles in road traffic by emitting ultrasonic signals and measuring the propagation delay. Prior to the measurement between the vehicles, cyclic transmission of a data telegram to all vehicles in the surroundings of the measurement takes place, the data telegram containing a time or time slots for the emission of ultrasonic signals.
The German laid-open specification DE 40 16 458 A1 describes another system for distance measurement between motor vehicles. In this case, information is transmitted in at least one direction by means of electromagnetic waves. In addition, acoustic impulses are transmitted in the opposite direction. The information transmitted by means of the electromagnetic waves contains information about the reception time of the acoustic impulse or about information derived therefrom. Communication between the vehicles can be effected using a time-division multiplexing system in this case.